32
G.E. Napolitano
characteristic fatty acid signatures, which allows an assessment of their contribution to the organic matter pool and to higher levels of the aquatic food web. Tables
2.4 and 2.5 present examples of ecological studies that used fatty acid markers to
trace trophic relationships and sources of organic matter, respectively.
Studies have shown that lipids from aquatic and terrestrial plants have different
and diagnostic fatty acids signatures and can therefore be used to characterize the
predominant energy source in aquatic systems. Although the dissolved and particulate lipids in the organic matter of lakes and other large bodies of water show
typical "aquatic fatty acid" profiles, lipids of terrestrial origin gradually become
more important with the proximity to land (Meyers et ai., 1984). This transition
from aquatic to terrestrial fatty acids is often reflected by the relative contribution
of medium-chain (~C 16) and longer-chain (~C26) fatty acids of phytoplankton
and terrestrial plants, respectively. Accordingly, the C 16/C26 fatty acid ratio in
the lipids of the POM of lakes increases with distance from land, reaching maximum values close to the bottom of the euphotic zone and farther from potential
sources of terrigenous materials (Meyers et ai., 1984).
The classification of the different inputs of organic carbon to aquatic ecosystem
can be complicated by the loss and transformation of the more labile components
due to physicochemical (Armstrong et ai., 1966) and biological processes (Meyers
et ai., 1984; Rhead et ai., 1971). During these processes, PUFAs (e.g., 18:3003,
18:4003, 18:5003,20:5003,22:6(03) are preferentially degraded, favoring the preservation of the less unsaturated and longer fatty acids of terrestrial plant origin (i.e.,
C20-C32 SAFAs and MUFAs) and ultimately altering the original fatty acid
profile (Meyers et ai., 1984). Other changes in the fatty acid composition of the
organic matter of aquatic systems may be the result of atmospheric transport of
particles and aerosols from distant sources. During precipitation, rainwater scavenges gases and aerosols that contain a vast array of organic materials of both
biogenic (Kawamura and Kaplan, 1983) and anthropogenic origins. Fatty acids are
an important fraction of the organic matter in rainwater, where they can exceed the
concentrations of ubiquitous hydrocarbons (n-alkanes) by a factor of 10 (Kawamura and Kaplan, 1983). Fatty acids in rainwater of a coastal area predominantly consisted of straight-chain compounds of C 12, C14, C16, and C18 of algal
origins and minor amounts of C20-C30 compounds from terrestrial plants (Kawamura and Kaplan, 1983).
2.4.6. Fatty Acids as Trophic Markers in Vertebrates
Comparative studies of fatty acid compositions have clearly shown that the concentrations of 18:2006 and 20:4006 in the lipids of freshwater animals are higher
than in their marine counterparts (Linko et ai., 1992; Muje et ai., 1989; GonzalezBaro and Pollero, 1988; Bell et ai., 1986; Kaitaranta and Linko, 1984). These
differences are related to mechanisms for the regulation of membrane fluidity and
the diet (see Landrum and Fisher, this volume). Ackman and Takeuchi (1986)
observed that in wild salmon (Salrno safar), the content of 20:4006 was six times
higher than in hatchery fish, and they suggested that this deficit may have been in
G.E. Napolitano
characteristic fatty acid signatures, which allows an assessment of their contribution to the organic matter pool and to higher levels of the aquatic food web. Tables
2.4 and 2.5 present examples of ecological studies that used fatty acid markers to
trace trophic relationships and sources of organic matter, respectively.
Studies have shown that lipids from aquatic and terrestrial plants have different
and diagnostic fatty acids signatures and can therefore be used to characterize the
predominant energy source in aquatic systems. Although the dissolved and particulate lipids in the organic matter of lakes and other large bodies of water show
typical "aquatic fatty acid" profiles, lipids of terrestrial origin gradually become
more important with the proximity to land (Meyers et ai., 1984). This transition
from aquatic to terrestrial fatty acids is often reflected by the relative contribution
of medium-chain (~C 16) and longer-chain (~C26) fatty acids of phytoplankton
and terrestrial plants, respectively. Accordingly, the C 16/C26 fatty acid ratio in
the lipids of the POM of lakes increases with distance from land, reaching maximum values close to the bottom of the euphotic zone and farther from potential
sources of terrigenous materials (Meyers et ai., 1984).
The classification of the different inputs of organic carbon to aquatic ecosystem
can be complicated by the loss and transformation of the more labile components
due to physicochemical (Armstrong et ai., 1966) and biological processes (Meyers
et ai., 1984; Rhead et ai., 1971). During these processes, PUFAs (e.g., 18:3003,
18:4003, 18:5003,20:5003,22:6(03) are preferentially degraded, favoring the preservation of the less unsaturated and longer fatty acids of terrestrial plant origin (i.e.,
C20-C32 SAFAs and MUFAs) and ultimately altering the original fatty acid
profile (Meyers et ai., 1984). Other changes in the fatty acid composition of the
organic matter of aquatic systems may be the result of atmospheric transport of
particles and aerosols from distant sources. During precipitation, rainwater scavenges gases and aerosols that contain a vast array of organic materials of both
biogenic (Kawamura and Kaplan, 1983) and anthropogenic origins. Fatty acids are
an important fraction of the organic matter in rainwater, where they can exceed the
concentrations of ubiquitous hydrocarbons (n-alkanes) by a factor of 10 (Kawamura and Kaplan, 1983). Fatty acids in rainwater of a coastal area predominantly consisted of straight-chain compounds of C 12, C14, C16, and C18 of algal
origins and minor amounts of C20-C30 compounds from terrestrial plants (Kawamura and Kaplan, 1983).
2.4.6. Fatty Acids as Trophic Markers in Vertebrates
Comparative studies of fatty acid compositions have clearly shown that the concentrations of 18:2006 and 20:4006 in the lipids of freshwater animals are higher
than in their marine counterparts (Linko et ai., 1992; Muje et ai., 1989; GonzalezBaro and Pollero, 1988; Bell et ai., 1986; Kaitaranta and Linko, 1984). These
differences are related to mechanisms for the regulation of membrane fluidity and
the diet (see Landrum and Fisher, this volume). Ackman and Takeuchi (1986)
observed that in wild salmon (Salrno safar), the content of 20:4006 was six times
higher than in hatchery fish, and they suggested that this deficit may have been in